Reactant stratification method for manufacturing articles made of polyurethane

ABSTRACT

An apparatus and method for manufacturing articles made of polyurethane that includes a mold assembly in communication with a mix chamber. The mix chamber is positioned below the mold assembly. The mix chamber includes a propeller for mixing the liquid polyurethane chemicals. The mix chamber further includes a pneumatically actuated bladder that causes the mixed chemicals to move from the mix chamber to the mold assembly. The chemicals expand to take on the shape of the mold. The method of the present invention comprises the steps of: (a) selecting polyurethane chemicals having certain specific weights; (b) placing said chemicals in a mix chamber wherein chemicals stratify according to their specific weights to prevent detrimental reaction among the chemicals until final mixing; and (c) allowing the chemicals to expand to form an article.

- This application is a continuation of application Ser. No. 08/451,743,filed on May 26, 1995, now abandoned, which is a divisional ofapplication Ser. No. 08/088,121, filed on Jul. 7, 1993, now U.S. Pat.No. 5,456,586.

BACKGROUND OF THE INVENTION

The present invention is directed to an apparatus and method formanufacturing articles made of polyurethane. More specifically, theinvention is directed to an apparatus having a mix chamber positionedbelow and in direct communication with a mold assembly.

Polyurethane foam has been used for many years for cushioning,insulation and other applications. Polyurethane foam is usuallymanufactured at atmospheric pressure from polyester or polyether basedpolyols combined with isocyanates, such as toluenediisocyanate (TDI),polymethylene polyphenylisocyanate (MDI), or mixtures thereof, andadditives to form a finished product ranging from a very flexible to avery rigid product. The cell structure of the foam can range fromcompletely open to completely closed. Examples of open cell, flexiblepolyurethane foam technology are disclosed in U.S. Pat. No. 4,451,583.

Expanded flexible polyurethane articles can be manufactured by thecontinuous conveyor method or by the molding method. Most expandedflexible polyurethane is currently produced by the continuous conveyormethod for producing slabs or by molding articles in a noncontinuousprocess. The continuous conveyer method or "slab-stock" method is usedto process the majority, by weight, of flexible polyurethane foam. Inthis method, the liquid chemicals are mixed together and poured on acarrier sheet of plastic or paper. The carrier sheet rests either on aconveyor flat floor with two vertical sides or on a conveyor with around shape. As the chemicals proceed down the conveyor, they rise orexpand in the form of closed cells. In the case of open cell foam, asthe reacting chemicals reach full expansion, the cell walls open andflow into struts. These struts continue to solidify until an almostcured dry article is formed. At the end of the conveyor, a saw cuts offa length of the article. The article is then taken to a storage area forfinal curing, which usually takes about 24 hours. This process iscontinuous until the machine is stopped.

In the alternative molding method, the liquid chemicals are mixed anddeposited in a mold, with or without a lid, and the chemicals expand tothe shape of the mold. It is important that the chemicals in a mold bemixed in a short interval of time so that the chemicals react properly.One common prior art molding method for large parts is known as the"bucket method". In the bucket method, a mix chamber for mixing theliquid chemicals is located above the interior of a separate mold. Thechamber is removed after the mixed chemicals are released in the mold.The chemicals expand and an article is formed in the mold. The bucketmethod has the disadvantage of being relatively complicated, difficultto clean, and produces foam full of blow holes. Further, the mix chamberin the bucket method is not in direct communication with the mold.

The present invention overcomes the disadvantages of the bucket methodwhile retaining the major bucket method advantage of mixing thechemicals all at once. The mix chamber in the present invention is indirect communication with the mold. The present invention can be usedalone to produce polyurethane articles with or without auxiliary blowingagents. It can also be used in a vacuum chamber to eliminate blowingagents as disclosed in my U.S. Pat. No. 5,182,313, the teachings ofwhich are incorporated herein by reference, or a positive pressurechamber depending on the application.

SUMMARY OF THE INVENTION

The present invention is directed to an apparatus and method formanufacturing articles made of polyurethane. The apparatus includes amold assembly in communication with a mix chamber. The mix chamber ispositioned below the mold assembly. The mix chamber includes a propellerfor mixing the liquid polyurethane chemicals. The mix chamber furtherincludes a pneumatically actuated bladder that causes the mixedchemicals to move from the mix chamber to the mold assembly. Thechemicals react in the mold assembly and expand to take on the shape ofthe mold. The method of the present invention comprises the steps of:(a) selecting polyurethane chemicals having certain specific weights;(b) placing the chemicals in a mix chamber wherein the chemicalsstratify according to their specific weights to prevent detrimentalreaction among the chemicals until final mixing; and (c) allowing saidchemicals to expand to form an article.

It is the primary object of the present invention to provide anapparatus and method for manufacturing a variety of articles made ofpolyurethane.

It is an important object of the present invention to provide anapparatus having a mix chamber positioned below and in directcommunication with a mold assembly.

Other objects and advantages of the invention will become apparent asthe invention is described hereinafter in detail and with reference tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side view of the apparatus of the present invention with thewalls of the mold assembly and the mix chamber partially cut away toshow the interior of the mold assembly and the mix chamber; and

FIG. 2 is a detailed side view of the mix chamber with the wallspartially cut away.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings, the apparatus of the present invention isidentified by reference numeral 10. The apparatus 10 includes a moldassembly 12. The mold assembly 12, which is preferably made of metalcomponents, includes a top cover 14 and a body 16. In the presentembodiment, the body 16 consists of a detachable wall 18 having acylindrical shape. However, it should be understood that the body 16 canbe formed in a variety of shapes and have any number of walls. The moldassembly includes a plastic liner 24 along the interior of the body 16.The liner 24 is fastened to the mold assembly 12 by upper and lowerresilient elastic members 30 and 32, respectively, that extend aroundthe exterior surface of the body 16. The plastic liner 24 can be made ofa variety of materials with polyethylene, polypropylene and polyvinylchloride plastics being preferred. The liner 24 has a thickness ofapproximately 0.025 to 0.25 mm with 0,125 mm being preferred,

The mold assembly includes a pump 34 that is in communication with theinterior of the mold assembly body 16 by a conduit 36. The conduit 36extends through the wall 18. When the pump 34 is actuated, air that isbetween the liner 24 and the interior of the body 16 is evacuatedthereby creating a vacuum in this space. The vacuum forces the liner toadhere to the interior of the body 16. This results in a smooth moldingsurface within the mold assembly 12.

The mix chamber 50 is shown in FIGS. 1 and 2. The mix chamber 50 ispositioned below the mold assembly 12. The chamber 50, which ispreferably made of metal components, includes a shell 52 having a base54 and an upwardly extending shell wail 56. The base 54 includes aninsert plug 57 held in position by threaded studs 58 and nuts 59. Theshell 52 is supported by a mix chamber frame 60 that includes a shellsupport member 62 and a propeller support member 64. The frame 60 alsoincludes a mold assembly support member 66. A flexible mold bottom liner68 is positioned between the support member 66 and the body 16. Theliner 68 is constructed of a durable plastic material similar to theliner 24 of the mold assembly 12.

Referring to FIG. 2, the base 54 of shell 52 includes at least oneopening for passage of polyurethane chemicals to the interior of theshell. In the present embodiment, the base includes a first opening 70for the passage of polyol and additives and a second opening 72 for thepassage of isocyanate. A conduit 74 extends through the first opening70. The conduit is in communication with a manifold 76. The manifold 76channels the flow of polyol and additives, such as water, amine,silicone and tin, from a polyol conduit 78 and additive conduits 80A-D.The conduits 78 and 80A-D are in communication with polyol and additivesources (not shown). The polyol and additives are moved by pumps 82 and84A-D, respectively.

A conduit 88 extends through the second opening 72. The conduit 88 is incommunication with a valve 90. The valve 90 is in communication with aconduit 92 that is connected to an isocyanate source (not shown). Themovement of the isocyanate is caused by a pump 94.

It should be understood that the liquid chemicals can be introduced fromthe bottom, as shown in the drawings, or from the top of the mix chamber50, or introduced from the top and bottom depending on the application.As described in detail below, the chemicals can be introduced to the mixchamber in various ways to stratify the individual chemicals to preventa detrimental reaction.

In the present embodiment, slow speed pumps (82 and 84A-D) are used toplace the chemicals in the mix chamber 50 through the base 54 of theshell 52. Slow speed pumps are relatively inexpensive and thus make theoverall apparatus less expensive to manufacture. The chemicals arepumped into the mix chamber 50 in a manner and sequence that, due to thespecific weight differences among the chemicals, they stratify such thatchemicals that react aggressively with each other are separated fromeach other by chemicals with which they do not react aggressively. Thisstratification separates the chemicals in a manner such that within thetime it takes to pump all the chemicals into the mix chamber using slowpumps no significant chemical reactions occur in the chemicals. Thestratification also allows the chemicals to rest in the mix chamber fora period of time without significant reaction.

Still referring to FIG. 2, the insert plug 57 of the base 54 includes anopening 96 through which extends a propeller shaft 98 connected at oneend to a motor 100 and at the other end to a propeller 102. An O-ring104 maintains proper alignment of the shaft 98 within the opening 96 andprovides a fluid-tight seal. The shaft 98 is connected to the motor 100by a coupling pin 106. The propeller 102 can include any number ofblades 108, with two being preferred. It should be understood thatvarious mixing devices can be used to mix the chemicals.

A bladder 110 covers at least a portion of the interior of the shell 52.In the present embodiment, the bladder 110 extends from the top edge 112of the shell wall 56 to a bottom edge 114 in the shell base 54. Thebladder 110 is secured to the shell 52 so that the space between thebladder 110 and the shell wall 56 is substantially fluid-tight. Thebladder 110 is constructed of a durable plastic material similar to theliner 24 of the mold assembly 12.

A passageway 120 extends through one of the shell walls 56. A conduit122 is in communication with the passageway 120. The conduit 122 is incommunication with a 3-way valve 124 that regulates the flow of a fluid,such as air, from pumps 126 and 128. The pump 126 causes air to flowthrough conduit 122 and into the space between the bladder 110 and theshell wall 56. The pump 128 creates a vacuum thereby evacuating air fromthe space. The movement of air into and out of the space causes thebladder 110 to expand and contract accordingly during the moldingprocess. As it will be readily apparent to one skilled in the art, theexpansion and contraction of the bladder 110 can also be donemechanically. Further, the flexible plastic bladder 110 as shown in thedrawings can be replaced by a relatively inflexible member incommunication with a mechanical device that could force the chemicalsfrom the mix chamber 50 to the mold assembly 12.

During the apparatus assembly process, the insert plug 57 is positionedin the base 54 over the bladder 110 that has been placed along edge 114.The nuts 59 are then threaded to studs 58 to affix the plug 57 to theshell support member 62. This forms a fluid-tight seal in the bottom ofthe bladder 110. The top of the bladder 110 is then folded over the edge112 of the shell wall 56. The pump 128 is activated to provide a vacuumto the space defined by the bladder 110 and the wall 56. The vacuumholds the bladder 110 tightly against the shell 52 and away from theblades 108 of the propeller 102 during the mixing of the chemicals.

The shaft 98 of the propeller 102 is inserted through opening 96 andattached to the motor 100. The polyol/additive conduit 74 and theisocyanate conduit 88 are then inserted in first opening 70 and secondopening 72, respectively. The shaft and conduits fit tightly withintheir respective openings to prevent leakage.

The mold bottom liner 68 is positioned on the upper surface of thesupport member 66 to form a fluid-tight seal with the bladder 110 at theedge 112 of the wall 56. The liner 24 of the mold assembly is thenpositioned in the interior of the body 16. Top and bottom portions ofthe liner 24 are folded to the exterior of the body 16 and fastened tothe exterior by elastic members 30 and 32, respectively. The moldassembly 12 is then positioned on top of and affixed to the mix chamber50 providing a fluid-tight seal. When so positioned, the top of theshell 52 is in direct communication with the interior of the moldassembly 12. The top cover 14 is placed on the mold assembly 12. Avacuum is then applied through the conduit 36 by the pump 34 to draw theliner 24 against the mold body 16.

During the molding process, polyol and additives are pumped into the mixchamber 50 through conduit 74 by pumps 82 and 84A-D through valve 76.Isocyanate is then pumped into the mix chamber 50 through conduit 88 bya pump 94 through valve 90. When all of the liquid chemicals are in thechamber 50, the motor 100 is activated to cause propeller 102 to rotate.The chemicals are then mixed through agitation by the propeller blades108. After the mixing is complete, the motor is deactivated. Thechemicals begin to rise from the mix chamber 50 into the mold assembly12. At the time the mixing cycle is complete, the valve 124 is switchedfrom the vacuum pump 128 to the positive pressure pump 126 by valve 124.This causes air to pass through the conduit 122 and into the spacedefined by the bladder 110 and the shell 52. As shown in FIG. 1, theexpansion of the bladder 110 forces the expanding chemicals out of themix chamber 50 and into the mold assembly 12 for final forming. Theelectrical control system that operates the pumps, valves, motor andcounters are not shown. The system is known in the art and is standardfor an apparatus of the type disclosed herein.

After curing of the formed article, the mold assembly is disassembledand the article is removed. The apparatus is then cleaned andreassembled as described above for subsequent molding operations.

EXPERIMENTAL DATA

Test formulas, physical properties and experimental data are set forthbelow.

    ______________________________________                                        TRIAL                                                                         Chemical       Proportion                                                                              Specific weight                                      ______________________________________                                        Polyol         4.94   kg     1.01                                             Water          .20    kg     1.00                                             Amine catalyst .01    kg     .87                                              Silicone       .10    kg     1.04                                             Tin            .01    kg     1.10                                             Isocyanate     2.42   kg     1.22                                             ______________________________________                                    

Polyol= 3000 molecular weight polyether triol with a functionality ofabout 3.1.

Isocyanate= toluene diisocyanate (TDI) with an 80-20 ratio of 2,4 and2,6 isomers.

All of the above proportions in the above chemical formula are byweight.

The specific weight listed for each chemical is the number thatexpresses the ratio between the weight of a given volume of listedsubstance and the weight of an equal volume of water.

EXAMPLE

The following example was produced in a cylindricaIly shaped mold thatwas 56 cm in diameter by 122 cm in height. The temperature of the moldwas maintained at a constant 21° C.

About 1.36 kg of polyol listed in the formula of Trial is pumped intothe mix chamber shell 52. All of the water, amine and silicone are thenseparately pumped into the shell 52. About 1.36 kg of polyol is thenpumped into the shell 52. All of the tin is then pumped into the shell52. The remaining polyol, about 2.22 kg, is then pumped into the shell52. All of the isocyanate is then pumped into the shell 52. Due to thespecific weights of the various chemicals, as stated above, they arestratified in layers in the mix chamber shell 52. This allowed thechemicals to be pumped into the shell 52 over a relatively long periodof time. It also allowed the chemicals to rest within the shell 52 for arelatively long period of time without a detrimental reaction.

When the forming process began, the mix motor 100 was activated causingthe propeller 102 to rotate at 600 rpm for approximately 15 seconds. Thechemicals were completely mixed. The chemicals listed in the formula ofTrial were selected and placed in the mix chamber 50 such that nodetrimental reaction occurred among them before mixing and they weremixed in a manner that assured that the reaction age throughout thearticle was uniform as it was being formed.

After mixing, the chemicals expanded and rose through the top opening ofthe shell 52 and into the mold assembly 12. At the time the mixingstopped, the valve 124 applied approximately 1 kg/cm² positive pressureon the bladder 110. This caused the bladder 110 to expand and force theexpanding chemicals out of the shell 52 and into the mold assembly 12.The expanding chemicals were formed into an article in the shape of themold.

The chemicals were allowed to cure for 10 minutes in the mold assembly12. The mold assembly was then disassembled and the finished article wasremoved. The apparatus 10 was then cleaned and reassembled for the nextmolding operation.

The above example produced an open cell flexible polyurethane articlehaving a density of 0.68 kg/m³. The core density was determined afterthe outer surface was removed from the molded article. The weight of thechemicals placed into the apparatus was sufficient to compensate for thehigh density of the removed outer surface and to compensate for theoff-gassing that occurred during the chemical reaction.

It should be understood that variations of the chemicals listed inTrial, with the exception of water, are available in other specificweights. Further, chemicals that perform substantially the same functionare available that react in different ways.

The above detailed description of the present invention is given forexplanatory purposes. It will be apparent to those skilled in the artthat numerous changes and modifications can be made in the example ofthe invention described above without departing from the scope of theinvention. Accordingly, the whole of the foregoing description is toconstrued in an illustrative and not a limitative sense, the scope ofthe invention being defined solely by the appended claims.

I claim:
 1. A method for the one-shot manufacture of articles made ofpolyurethane, which comprises the steps of:(a) selecting polyurethanechemicals from a group consisting of polyol, isocyanate and selectedadditives, each of said selected chemicals having a certain specificweight; (b) placing said chemicals into a mix chamber with water whereinsaid chemicals and water stratify in layers according to their specificweights to prevent detrimental reaction among said chemicals, whereinthe water layer and the isocyanate layer are separated; and (c) mixingsaid chemicals and water to cause said chemicals to react and expandinto a mold assembly to form an article.
 2. The method of claim 1,wherein said mix chamber has a top and a bottom and said chemicals areplaced in said mix chamber from said bottom of said mix chamber.
 3. Themethod of claim 1, wherein said mix chamber has a top and a bottom andsaid chemicals are placed in said mix chamber from said top of said mixchamber.
 4. A method for the one-shot manufacture of articles made ofpolyurethane which comprise the steps of:(a) selecting desired amountsof polyol, water, silicone and specified catalysts, all having knownspecific weights; (b) selecting a desired amount of isocyanate having aknown specific weight; (c) placing the desired amounts of polyol,isocyanate, water, silicone and specified catalysts into a mix chamberin stratified layers to prevent detrimental reaction until mixing,wherein the water layer and isocyanate layer are separated; (d) mixingthe polyol, catalysts, water, silicone and isocyanate to create apolyurethane mix; (e) expanding the polyurethane mix from the mixchamber to a mold cavity; and (f) removing the formed polyurethanearticle from the mold cavity.
 5. The method of claim 4, wherein thepolyol, catalysts, water, silicone and isocyanate are placed into themix chamber from the bottom of the mix chamber.
 6. The method of claim4, wherein the polyol, catalysts, water, silicone and isocyanate areplaced into the mix chamber from the top of the mix chamber.
 7. Themethod of claim 4, wherein the step of expanding the polyurethane mixincludes the application of fluid pressure to a flexible bladder memberto expand and force the polyurethane mix from the mix chamber to themold cavity.
 8. The method of claim 4, wherein the step of expanding thepolyurethane mix includes the application of fluid pressure to anexpansible member to expand and force the polyurethane mix from the mixchamber to the mold cavity.
 9. A method for the one-shot manufacture ofarticles made of polyurethane which comprises the steps of:(a) selectingdesired amounts of polyol, water, silicone and specified catalysts, allhaving known specific weights; (b) selecting a desired amount ofisocyanate having a known specific weight; (c) selecting a mold chamberof predetermined shape; (d) lining a mix chamber with a thin flexibleliner smoothly engaged with the walls of the mix chamber; (e) engagingthe mix chamber with the mold chamber; (f) placing the desired amountsof polyol, isocyanate, water, silicone and specified catalysts into themix chamber in stratified layers to prevent detrimental reaction untilmixing, wherein the water layer and isocyanate layer are separated; (g)mixing the polyol, catalysts, water, silicone and isocyanate to create apolyurethane mix; (h) expanding the polyurethane mix from the mixchamber to the mold chamber; and (i) removing the formed polyurethanearticle from the mold chamber.
 10. The method of claim 9, wherein thepolyol, catalysts, water, silicone and isocyanate are placed into themix chamber from the bottom of the mix chamber.
 11. The method of claim9, wherein the polyol, catalysts, water, silicone and isocyanate areplaced into the mix chamber from the top of the mix chamber.
 12. Themethod of claim 9, wherein the step of expanding the polyurethane mixincludes the application of fluid pressure to a flexible bladder memberto expand and force the polyurethane mix from the mix chamber to themold chamber.
 13. The method of claim 9, wherein the step of expandingthe polyurethane mix includes the application of fluid pressure to anexpansible member to expand and force the polyurethane mix from the mixchamber to the mold chamber.
 14. A method for the one-shot manufactureof articles made of polyurethane, which comprises the steps of:(a)selecting polyurethane chemicals from a group consisting of polyol,isocyanate and selected additives, each of said selected chemicalshaving a certain specific weight; (b) placing said chemicals into a mixchamber with water wherein said chemicals and water stratify in layersaccording to their specific weights to prevent detrimental reactionamong said chemicals, wherein the water layer and the isocyanate layerare separated; (c) mixing said chemicals and water to cause saidchemicals to react and form a polyurethane mix; and (d) placing saidpolyurethane mix into a mold assembly to form a molded polyurethanearticle.